This PR adds the Ruby 3.1 and Rails 7 elements to the CI matrix. To support those changes a number of other changes were required:
- Adding a basic Rails 7 Gemfile and updating `Appraisals`
- Quoting 3.0 in the `.github/workflows/build.yml` file so that this entry pulls Ruby 3.0.x and not Ruby 3.1
- Adding the "--disable-error_highlight" value for RUBYOPT in the build environment to disable Ruby 3.1 error highlighting
- Bumping the version of `standard` and configuring it to run against our oldest supported version
Peter Goldstein